Subject: Re: [RFC PATCH V4] pci: virtio_pci: Add SR-IOV support for virtio_pci devices

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 27 Feb 2018 00:32:47 +0200

On Mon, Feb 26, 2018 at 07:26:14AM -0800, Alexander Duyck wrote:
> On Sun, Feb 25, 2018 at 8:48 PM, Mark Rustad <[email-masked]> wrote:
> > Hardware-realized virtio_pci devices can implement SR-IOV, so this
> > patch enables its use. The device in question is an upcoming Intel
> > NIC that implements both a virtio_net PF and virtio_net VFs. These
> > are hardware realizations of what has been up to now been a software
> > interface.
> >
> > The device in question has the following 4-part PCI IDs:
> >
> > PF: vendor: 1af4 device: 1041 subvendor: 8086 subdevice: 15fe
> > VF: vendor: 1af4 device: 1041 subvendor: 8086 subdevice: 05fe
> >
> > The patch needs no check for device ID, because the callback will
> > never be made for devices that do not assert the capability or
> > when run on a platform incapable of SR-IOV.
> >
> > One reason for this patch is because the hardware requires the
> > vendor ID of a VF to be the same as the vendor ID of the PF that
> > created it. So it seemed logical to simply have a fully-functioning
> > virtio_net PF create the VFs. This patch makes that possible.
> >
> > Signed-off-by: Mark Rustad <[email-masked]>
> > Reviewed-by: Alexander Duyck <[email-masked]>
> 
> Mark,
> 
> In the future please don't put my "Reviewed-by" on a patch that I
> haven't reviewed. I believe I reviewed one of the earlier patches, but
> I hadn't reviewed this version.
> 
> Also, after thinking about it over the weekend we may want to look at
> just coming up with a truly "generic" solution that is applied to
> SR-IOV capable devices that don't have a SR-IOV capable driver loaded
> on them. That would allow us to handle the uio, vfio, pci-stub, and
> virtio cases all in one fell swoop. I think us going though and
> modifying one patch at a time to do this kind of thing isn't going to
> scale.

uio really can't support VFs properly - without proper IOMMU
support any MSIs can corrupt kernel memory, and VFs are
limited to MSIs.

> I'll try to do some digging and find the VFIO approach we had been
> working on. I think with a couple tweaks we can probably make that
> truly generic and ready for submission.
> 
> Thanks.
> 
> - Alex
> 
> > ---
> > Changes in V4:
> > - V3 was a mis-send, this has what was intended
> > - Move most code to new helpers in pci/iov.c, pci_sriov_configure_generic
> >   and pci_sriov_disable_generic
> > - Correct mislabeling of vendor and device IDs
> > - Other minor changelog fixes
> > - Rebased to pci/master, since most changes are in that area now
> > - No new ifdefs with this approach (yay)
> > Changes in V3:
> > - Missent patch, please disregard
> > Changes in V2:
> > - Simplified logic from previous version, removed added driver variable
> > - Disable SR-IOV on driver removal except when VFs are assigned
> > - Sent as RFC to virtio-dev, linux-pci, netdev, lkml and others
> > ---
> >  drivers/pci/iov.c                  |   50 ++++++++++++++++++++++++++++++++++++
> >  drivers/virtio/virtio_pci_common.c |    2 +
> >  include/linux/pci.h                |   10 +++++++
> >  3 files changed, 62 insertions(+)
> >
> > diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> > index 677924ae0350..4b110e169b7c 100644
> > --- a/drivers/pci/iov.c
> > +++ b/drivers/pci/iov.c
> > @@ -367,6 +367,56 @@ static void sriov_disable(struct pci_dev *dev)
> >         pci_iov_set_numvfs(dev, 0);
> >  }
> >
> > +/**
> > + * pci_sriov_disable_generic - standard helper to disable SR-IOV
> > + * @dev:the PCI PF device whose VFs are to be disabled
> > + */
> > +int pci_sriov_disable_generic(struct pci_dev *dev)
> > +{
> > +       /*
> > +        * If vfs are assigned we cannot shut down SR-IOV without causing
> > +        * issues, so just leave the hardware available.
> > +        */
> > +       if (pci_vfs_assigned(dev)) {
> > +               pci_warn(dev,
> > +                        "Cannot disable SR-IOV while VFs are assigned - VFs will not be deallocated\n");
> > +               return -EPERM;
> > +       }
> > +       pci_disable_sriov(dev);
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_sriov_disable_generic);
> > +
> > +static int pci_sriov_enable(struct pci_dev *dev, int num_vfs)
> > +{
> > +       int rc;
> > +
> > +       if (pci_num_vf(dev))
> > +               return -EINVAL;
> > +
> > +       rc = pci_enable_sriov(dev, num_vfs);
> > +       if (rc) {
> > +               pci_warn(dev, "Failed to enable PCI sriov: %d\n", rc);
> > +               return rc;
> > +       }
> > +       pci_info(dev, "SR-IOV enabled with %d VFs\n", num_vfs);
> > +       return num_vfs;
> > +}
> > +
> > +/**
> > + * pci_sriov_configure_generic - standard helper to configure SR-IOV
> > + * @dev: the PCI PF device that is configuring SR-IOV
> > + */
> > +int pci_sriov_configure_generic(struct pci_dev *dev, int num_vfs)
> > +{
> > +       if (num_vfs)
> > +               return pci_sriov_enable(dev, num_vfs);
> > +       if (!pci_num_vf(dev))
> > +               return -EINVAL;
> > +       return pci_sriov_disable_generic(dev);
> > +}
> > +EXPORT_SYMBOL_GPL(pci_sriov_configure_generic);
> > +
> >  static int sriov_init(struct pci_dev *dev, int pos)
> >  {
> >         int i, bar64;
> > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> > index 48d4d1cf1cb6..d7679377131f 100644
> > --- a/drivers/virtio/virtio_pci_common.c
> > +++ b/drivers/virtio/virtio_pci_common.c
> > @@ -584,6 +584,7 @@ static void virtio_pci_remove(struct pci_dev *pci_dev)
> >         else
> >                 virtio_pci_modern_remove(vp_dev);
> >
> > +       pci_sriov_disable_generic(pci_dev);
> >         pci_disable_device(pci_dev);
> >         put_device(dev);
> >  }
> > @@ -596,6 +597,7 @@ static struct pci_driver virtio_pci_driver = {
> >  #ifdef CONFIG_PM_SLEEP
> >         .driver.pm      = &virtio_pci_pm_ops,
> >  #endif
> > +       .sriov_configure = pci_sriov_configure_generic,
> >  };
> >
> >  module_pci_driver(virtio_pci_driver);
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 024a1beda008..937124d4e098 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -1947,6 +1947,8 @@ int pci_iov_virtfn_devfn(struct pci_dev *dev, int id);
> >
> >  int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn);
> >  void pci_disable_sriov(struct pci_dev *dev);
> > +int pci_sriov_disable_generic(struct pci_dev *dev);
> > +int pci_sriov_configure_generic(struct pci_dev *dev, int num_vfs);
> >  int pci_iov_add_virtfn(struct pci_dev *dev, int id);
> >  void pci_iov_remove_virtfn(struct pci_dev *dev, int id);
> >  int pci_num_vf(struct pci_dev *dev);
> > @@ -1973,6 +1975,14 @@ static inline int pci_iov_add_virtfn(struct pci_dev *dev, int id)
> >  static inline void pci_iov_remove_virtfn(struct pci_dev *dev,
> >                                          int id) { }
> >  static inline void pci_disable_sriov(struct pci_dev *dev) { }
> > +static inline int pci_sriov_disable_generic(struct pci_dev *dev)
> > +{
> > +       return -ENODEV;
> > +}
> > +static inline int pci_sriov_configure_generic(struct pci_dev *dev, int num_vfs)
> > +{
> > +       return -ENODEV;
> > +}
> >  static inline int pci_num_vf(struct pci_dev *dev) { return 0; }
> >  static inline int pci_vfs_assigned(struct pci_dev *dev)
> >  { return 0; }
> >